The invention relates to a cathode having a supporting body substantially consisting of nickel and being coated with a layer of electron-emissive material comprising alkaline earth metal oxides and barium.
Such cathodes are generally known and are described, for example in "Advances in Electronics and Electron Physics, 25, 211-275 (1968). The emission of such cathodes is dependent on releasing barium from the alkaline earth metal oxide barium oxide the alkaline earth metal oxide. In addition to the barium oxide, the electron-emissive material usually comprises strontium oxide and sometimes calcium oxide.
In practice the actual emission is substantially from by small regions (so-called "sites") spread over the electron-emissive material and having the lowest effective work function for electrons. regions having a slightly higher work function will hardly contribute to the electron current generated by the cathode.